The present invention relates to a peak detector and more specifically to a peak detector design for low amplitude wide band AC signals.
An AC peak detector is a non-linear circuit used to obtain a steady state amplitude at the level of the peak amplitude of the input AC signal. The input AC signal may not be a uniform sinusoid, an infinite sum of sinusoids as in a square wave signal, but any signal with approximately complimentary positive and negative voltage peaks, +VPK and xe2x88x92VPK such as a data communication signal or a signal used from an HDD or a DVD system. A number of different peak detector designs are known. However, each design has shortcomings within which limit the range of operability and performance within that range. In particular there is a need for peak detectors which detect peaks with amplitude as low as 50 or even 20 millivolts.
In disks such as DVD or DVD-RAM, information is recorded in sector units. Each sector unit is comprised of a header information area having physical information data (PID) area and user data area. The header information area is divided into a peak header area and a bottom header area, and the user data area is divided into a land area and a groove area.
Fingerprints, dust and scratches on the disk result in noise being generated in the DVD recording playback system. Consequently, there is a need for limiting the effects of this noise in both magnitude and duration of the noise. In FIG. 1, a comparator 100 accepts an input signal, and this input signal is compared with the output signal. The output of the comparator 100 produces a pulse whenever the input signal exceeds the output signal or whenever a new peak occurs. The output of comparator 100 is connected to current source 102 to control the output of current source 102, and capacitor 104. The comparator 100 controls the current generator current source in such a manner to produce more current when the pulses are generated from capacitor 100 or more particularly when the input voltage exceeds the output voltage. The current flows from current source 102 to capacitor 104 where the current charges the capacitor 104 to a point where the output voltage is equal to the input voltage at which time the comparator 100 ceases output.
The output pulses and consequently the current generator 102 remain at a constant level and the voltage remains at the new peak. FIG. 2 illustrates the effect of a large noise signal to the circuit of FIG. 1. The output voltage follows the magnitude of the noise signal and the duration before the output voltage again begins to follow the peaks is significantly long. The length of time is due to the fact that it takes a significant amount of time before decay sets in as a result of capacitor 104 and the constant current source 106.
The present invention provides a peak detector which suppresses noise both in amplitude and duration. The present invention substantially reduces the duration that the effects of noise has on the output voltage. The present invention uses a bias voltage to operate a transistor so that a constant current places a charge on a capacitor to prevent the undesirable effects of a large input voltage in the form of noise.